Over the past several years there have been increasing demands placed upon graphics subsystems in all variety of hardware. For example, in the general computing area, even traditionally mundane programs, like presentation software, are including animation and other tools that are requiring faster and more complex graphics computation. In addition, the traditional graphics-intense applications like video, photo editing and gaming are growing both in scope and graphics-intensity. Moreover, vertical systems such as gaming and graphics dedicated computing (e.g. Nintendo Gamecube etc.) have accelerated even faster driving competition with the general computing architecture for graphics supremacy.
During this same time period, hardware manufacturers have sought to meet and exceed the growing demand with dedicated graphics processors having ever-increasing capability. Right now, there are several commercially available graphics processing units (GPUs) that are programmable. While both programmable and non-programmable GPUs offer enhanced speed for graphics calculations, programmable GPUs differ in that they offer a high measure of flexibility. For example, prior to programmable GPUs, an application programmer might decide between using CPU time to render a more interesting graphic or using the GPU to increase overall application performance at the cost of displaying a less ideal graphic. Programmable GPUs have combined the speed advantage of prior GPUs with a significant measure of flexibility. In practical terms, programmability is an important advantage because it allows programs to use the graphics chip in ways similar to the system microprocessor. By using the GPU this way, the system can generate virtually infinite graphics effects without loading the system CPU.
Programmable GPUs run programs that are generally called fragment programs. The name “fragment” program derives from the fact that the unit of data being operated upon is generally a pixel—i.e a fragment of an image. The GPUs can run a fragment program on several pixels simultaneously to create a result which is generally referred to by the name of the buffer in which it resides. GPUs use data input generally called textures, which is analogous to a collection of pixels.
Also, during the same time period that GPUs were contemplated and developed, there have been efforts under way to provide some programming interfaces for application programs desiring to use the graphics-dedicated hardware. One such effort is commonly known as OpenGL. The goal of OpenGL is to make graphic function accessible to the programmer independent of the hardware. In doing so, OpenGL operates like a state machine. In particular, a program using the OpenGL library must set states such as current color, lighting, blending etc. When the program is run, the resultant context will be a combination of the states and input textures, such combination depending upon what was programmed. Given the state machine type operation, the result of an operation isn't always readily predictable.
As computers migrate toward more visually rich content, image processing becomes more important. As a consequence, the programmer's ease of accessing these tools and the efficiency of graphics calculations continues to grow in importance. While the combination of OpenGL and programmable GPUs have provided wide advances to graphics programmability, there remains a need for a higher level interface to the graphics subsystem. This need is heightened for applications directly involved in image processing (e.g. PhotoShop, AfterEffects or similar software). In these applications and others, it is desirable to have an abstraction layer that hides the complexity of graphics hardware from those exploiting that infrastructure. Furthermore, operating systems may wish to facilitate an overall rich user graphics experience by presenting such an abstraction layer to all applications.
Such an interface should allow a programmer or program to simply apply a filter or effect to a given image. Implicit in the need for a higher level API is the need to implement that API in a way that is both fast and efficient. In order to be efficient, a system should have a mechanism to conceptualize graphics programming in a way that is easy to understand and easy to operate upon. Furthermore, such a system should minimize the use of memory and computation time, while also efficiently dividing work between the CPU and GPU. Finally, it is desirable to have a system that may be emulated on a single processor so that programs built for dual processor systems (GPU and CPU) can run on legacy systems having only a CPU.